Spiral Gate Positioning for Hard Disk Drive Self-Servo Writing
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Solution Overview
Problem
Current spiral-based self-servo writing methods in hard disk drives face challenges with robust spiral detection due to high non-repeatable runout (NRRO), leading to missed spiral detection, especially when using widely spaced spirals.
Innovation Solution
The method involves timing the spiral gate for monitoring a reference spiral based on the radial position and radial velocity of the magnetic head when crossing the preceding spiral, allowing for accurate estimation and timing of the next spiral crossing to avoid missed detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If windowed spiral demodulation is used to reduce stray signal interference, then reliability of spiral detection is improved, but measurement precision deteriorates due to missed spiral detection under high NRRO
Solution Approach 1:
The spiral gate timing is made dynamic by adjusting it based on measured radial position and radial velocity from the preceding spiral crossing. This allows the gate to adapt to NRRO variations while maintaining fixed duration, resolving the contradiction between reliability and precision
Solution Approach 2:
The system uses feedback from measured radial position and radial velocity at the preceding spiral crossing to predict and adjust the timing of the next spiral gate. This feedback mechanism enables accurate detection despite NRRO while maintaining the benefits of windowed demodulation
2Productivity
If spiral gate timing is advanced based on radial position and velocity measurements, then productivity of spiral detection is improved, but device complexity increases due to additional measurements and calculations
Solution Approach 1:
The system uses its own existing measurements of radial position and radial velocity from the preceding spiral crossing to adjust timing, rather than requiring external or additional complex measurement systems. The read channel's existing capabilities are leveraged to improve detection accuracy
Solution Approach 2:
The timing parameter of the spiral gate is adjusted based on changes in radial position and radial velocity measurements. By modifying this single critical parameter dynamically, the system achieves higher detection accuracy without substantially increasing overall device complexity
Data Source
AI summary
A magnetic write head is positioned based on position signals generated by a read head as the read head crosses a plurality of reference spirals. The spiral gate for monitoring a particular reference spiral is timed to begin at a time based on the radial position of the magnetic head when crossing the preceding reference spiral. In this way, the spiral crossing time for the particular reference spiral can be estimated with sufficient accuracy that the spiral gate coincides with the magnetic head crossing the particular reference spiral. Consequently, spiral detection is assured, even in the presence of large non-repeatable runout.